SAN FRANCISCO—Researchers have found evidence to suggest that tumor necrosis factor receptor II (TNFRII) may be an important driver of cutaneous T-cell lymphomas (CTCLs).
The team discovered that a mutation in this receptor—TNFRII T377I—is present in patients with mycosis fungoides (MF) and those with Sézary syndrome (SS).
And previous research showed that the region encoding TNFRII on chromosome 1 is sometimes amplified in MF and SS patients.
So if, as these factors suggest, TNFRII does play a key role in CTCL, a number of currently available drugs—including proteasome inhibitors and MEK inhibitors—may be effective treatment options.
Alexander Ungewickell, MD, PhD, of Stanford University in California, discussed this possibility and the research supporting it at the 6th Annual T-cell Lymphoma Forum.
A novel mutation
Dr Ungewickell and his colleagues began this research by conducting transcriptome sequencing on samples from 3 patients with SS (Lee et al, Blood 2012). This revealed about 500 genes that were upregulated and about 500 that were downregulated in SS cells.
And pathway enrichment analysis showed that molecular mechanisms of cancer were the most significantly altered pathways. But the researchers also observed PI3 kinase signaling, T-cell receptor signaling, regulation of IL-2, and CD8 signaling.
To better understand the basis for these transcriptional changes, the team performed whole-exome sequencing in 11 CTCL-normal pairs. They uncovered an average of 46 mutations per exome, as well as pathways similar to those observed in the transcriptional analysis.
The researchers then used this information to generate a 245-gene capture reagent. And they used that to perform ultra-deep targeted resequencing on 83 samples from CTCL patients.
“Two things that stood out right away were that TNFRSF1B and KRAS had recurrent point mutations that suggested an activating phenotype,” Dr Ungewickell said. “It’s already known that KRAS is mutated in many human cancers, including CTCL. TNFRSF1B encodes TNFRII and was not previously associated with any malignancies.”
“We also found a smattering of other genes that were mutated, [but] we were most interested in the TNFRII mutation because of the novelty of the finding and also the potential for therapeutic intervention.”
Driving disease
Dr Ungewickell noted that TNFRII is expressed in CD4 and CD8 T lymphocytes but relatively few other cell types. TNFRII is activated by membrane-bound TNFα, which mediates the signal through TRAF proteins and CIAP proteins to activate the NF-κB-inducing kinase (NIK).
This activates the I kappa B kinase (IKK) complex to phosphorylate p100. When phosphorylated, it is processed in the proteasome and translocates to the nucleus. There, it interacts with RelB to mediate transcription that tends to cause T-cell activation and proliferation.
TNFRII also binds to TRAF2 and induces its degradation. The recurrent mutation the researchers identified in TNFRII (T377I) is in the TRAF2 regulatory domain in an evolutionarily conserved residue.
The ultra-deep targeted resequencing of 83 CTCL samples showed 4 mutations at that locus, all of which were acquired in the lymphoma.
This suggests TNFRII is important in CTCL. And the researchers hypothesized that, if that’s the case, TNFRII might be overexpressed in SS cells. So they looked at their transcriptome data and found TNFRII to be overexpressed in all 3 patients.
“Interestingly, the region that encodes TNFRII on chromosome 1 is also amplified in 1 of the 4 commonly used CTCL cell lines, suggesting that amplification may be another way of activating this pathway,” Dr Ungewickell said.
“And we were very interested by a study published by van Doorn et al a few years ago [Blood 2009], which showed that that region of chromosome 1 p36 is, in fact, amplified in 45% of cases of MF and 15% of cases of Sézary syndrome.”
“So we are currently doing FISH studies to confirm that this receptor is actually amplified in as many as half of cases of MF, suggesting that maybe, between mutation and amplification, this is an important driver of CTCL.”
Therapeutic possibilities
The researchers also thought that, if TNFRII is an important driver of CTCL, there would be some kind of transcriptional mark on the lymphoma cells. So they performed gene set enrichment analyses on 24 CTCL samples that had undergone 3-seq.
By comparing tumors expressing high levels of TNFRII and those expressing low levels of TNFRII, the team identified an expression signature that corresponds to the receptor’s known effects on RNA levels in T cells.
When they searched publicly available datasets, the researchers found this signature in 63 cases of MF (Shin et al, Blood 2007). And results of control experiments suggested the signature is specific to CTCL.
“If TNFRII is more active [in CTCL] and the mutation that we found is a hyperactivating mutation, we would expect this pathway to show increased activity downstream; namely, you would expect more processing of p100 to p52,” Dr Ungewickell said.
To investigate this possibility, the researchers generated Jurkat cells expressing empty vector, wild-type TNFRII, or mutant TNFRII and looked at NF-κB processing. They did see an increase in processing with the mutant receptor, compared to the wild-type receptor or empty vector.
“We also found, somewhat surprisingly, increases in phospho-ERK with the mutant receptor, as well as phospho-MEK,” Dr Ungewickell said.
“And to our knowledge, the RAS/MAP kinase pathway has not previously been linked to TNFRII signaling, suggesting that there is some kind of direct or indirect cross-talk between these pathways. We think it’s very interesting, since there are KRAS mutations that activate the RAS/MAP kinase pathway in a subset of these cases, suggesting some kind of synergy.”
Introducing the mutant receptor into primary CD4+ T cells had an effect similar to that observed in the Jurkat cells. The researchers did western blotting for NF-kB processing, and they saw an increase in p100 to p52 processing.
“This is a preliminary experiment, but we’re actually quite excited about this, since Jurkat cells have many abnormalities, due to the fact that they’re a leukemia line, and primary T cells will have the rest of the genome intact,” Dr Ungewickell said.
Now, he and his colleagues are conducting several studies to identify the changes that occur in primary T cells when mutant TNFRII is expressed. They also want to see if they can recapitulate CTCL and identify the transcriptional signature they previously found in patient biopsies and cells.
Lastly, the researchers are performing functional assays to evaluate proliferation, apoptosis, and pharmacological information, with the goal of identifying therapies that might be effective in patients with TNFRII mutation or amplification.
“Patients who have increased TNFRII signaling might respond to proteasome inhibitors, since p100 and p52 processing requires the proteasome,” Dr Ungewickell said. “And given that cross-talk with the RAS/MAP kinase signaling, as well as the KRAS mutations, we also think . . . that MEK inhibitors might be effective in the treatment of CTCL.”
